Chemical vapor deposition process for depositing titanium nitride films from an organo-metallic compound

ABSTRACT

A process for depositing titanium nitride films containing less than 5% carbon impurities and less than 10% oxygen impurities by weight via chemical vapor deposition is disclosed. Sheet resistance of the deposited films is generally within a range of about 1 to 10 ohms per square. The deposition process takes place in a deposition chamber that has been evacuated to less than atmospheric pressure and utilizes the organo-metallic compound tertiary-butyltris-dimethylamido-titanium and a nitrogen source as precursors. The deposition temperature, which is dependent on the nitrogen source, is within a range of 350° C. to 700° C. The low end of the temperature range utilizes nitrogen-containing gases such as diatomic nitrogen, ammonia, hydrazine, amides and amines which have been converted to a plasma. The higher end of the temperature range relies on thermal decomposition of the nitrogen source for the production of reaction-sustaining radicals. In such a case, the use of diatomic nitrogen gas is precluded because of its high dissociation temperature. Other materials may be simultaneously incorporated in the titanium nitride films during either embodiment of the deposition process as heretofore described. For example, a titanium nitride film incorporating aluminum and having the general formula TiAlN may be deposited by introducing aluminum-containing compounds. Additionally, a titanium nitride film incorporating tungsten and having the general formula TiNW may be deposited by introducing tungsten-containing compounds.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 10/032,655,filed Oct. 28, 2001, now U.S. Pat. No. 6,531,192, issued Mar. 11, 2003,which is a continuation of application Ser. No. 09/148,373, filed Sep.4, 1998, now U.S. Pat. No. 6,338,880 B1, issued Jan. 15, 2002, which isrelated to application Ser. No. 09/148,371, filed Sep. 4, 1998, now U.S.Pat. No. 6,168,837, issued Jan. 2, 2001.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to integrated circuit fabrication technology and,more specifically, to processes for depositing titanium nitride filmsvia chemical vapor deposition.

2. State of the Art

The compound titanium nitride (TiN) has numerous potential applicationsbecause it is extremely hard, chemically inert (although it readilydissolves in hydrofluoric acid), is an excellent conductor, possessesoptical characteristics similar to those of gold, and has a meltingpoint around 3000° C. This durable material has long been used to gildinexpensive jewelry and other art objects. However, during the last tento twelve years, important uses have been found for TiN in the field ofintegrated circuit manufacturing. Not only is TiN unaffected byintegrated circuit processing temperatures and most reagents, it alsofunctions as an excellent barrier against diffusion of dopants betweensemiconductor layers. In addition, TiN also makes excellent ohmiccontact with other conductive layers.

In a common application for integrated circuit manufacture, a contactopening is etched through an insulative layer down to a diffusion regionto which electrical contact is to be made. Titanium metal is thensputtered over the wafer so that the exposed surface of the diffusionregion is coated. The titanium metal is eventually converted to titaniumsilicide, thus providing an excellent conductive interface at thesurface of the diffusion region. A titanium nitride barrier layer isthen deposited, coating the walls and floor of the contact opening.Chemical vapor deposition of tungsten or polysilicon follows. In thecase of tungsten, the titanium nitride layer provides greatly improvedadhesion between the walls of the opening and the tungsten metal. In thecase of the polysilicon, the titanium nitride layer acts as a barrieragainst dopant diffusion from the polysilicon layer into the diffusionregion.

At least five processes are presently used for creating thin titaniumnitride films: (1) reactive sputtering; (2) annealing of asputter-deposited titanium layer in a nitrogen ambient; (3) ahigh-temperature atmospheric pressure chemical vapor deposition (APCVD)process, using titanium tetrachloride, nitrogen and hydrogen asreactants; (4) a low-temperature APCVD process, using ammonia andtetrakis-dialkylamido-titanium compounds which have the generic formulaTi(NR₂)₄ as precursors; and (5) a low-pressure chemical vapor deposition(LPCVD) process, using tetrakis-dialkylamido-titanium compounds as thesole precursor. FIG. 1 depicts the structural formula oftetrakis-dialkylamido-titanium. Each of the “R” groups may be as simpleas a methyl group (CH₃—) or they may be more complex alkyl groups. Eachof the processes enumerated above has its associated problems.

Both reactive sputtering and nitrogen ambient annealing of depositedtitanium result in films having poor step coverage, which are notuseable in submicron processes. Chemical vapor deposition processes havean important advantage in that conformal layers of any thickness may bedeposited. This is especially advantageous inultra-large-scale-integration circuits, where minimum feature widths maybe smaller than 0.3 μm. Layers as thin as 10 Å may be readily producedusing CVD. However, TiN coatings prepared using the high-temperatureAPCVD process must be prepared at temperatures between 900-1000° C. Thehigh temperatures involved in this process are incompatible withconventional integrated circuit manufacturing processes. Hence,depositions using the APCVD process are restricted to refractorysubstrates such as tungsten carbide. The low-temperature APCVD, on theother hand, though performed within a temperature range of 100-400° C.that is compatible with conventional integrated circuit manufacturingprocesses, is problematic because the precursor compounds (ammonia andTi(NR₂)₄) react spontaneously in the gas phase. Consequently, specialprecursor delivery systems are required to keep the gases separatedduring delivery to the reaction chamber. In spite of special deliverysystems, the highly spontaneous reaction makes full wafer coveragedifficult to achieve. Even when achieved, the deposited films tend tolack uniform conformality, are generally characterized by poor stepcoverage, and tend to deposit on every surface within the reactionchamber, leading to particle problems. A problem with the LPCVD processis that the deposited TiN films are high in carbon content even if theprecursor is limited to tetrakis-dialkylamido-titanium, the compound ofthe group which contains the fewest carbon atoms. The carbon atomswithin the precursor molecules are incorporated into the film as theprecursor molecules dissociate. Although it is possible to reduce thecarbon content of the films by annealing them in ammonia and nitrogengases, the films attain neither the purity nor the conductivity ofsputtered films.

What is needed is a new chemical vapor deposition process which willprovide highly conformal TiN films of high purity and with step coveragethat is suitable for sub-0.25 μm generations of integrated circuits.

BRIEF SUMMARY OF THE INVENTION

This invention includes various processes for depositing titaniumnitride films containing less than 5 percent carbon impurities and lessthan 10 percent oxygen impurities by weight via chemical vapordeposition and the use of a metal-organic precursor compound. Sheetresistance of the deposited films is within a range of about 1 to 10ohms per square. The deposition process takes place in a depositionchamber that has been evacuated to less than atmospheric pressure andutilizes the organo-metallic compoundtertiary-butyltris-dimethylamido-titanium (TBTDMAT) and a nitrogensource as precursors. The compoundtertiary-butyltris-dimethylamido-titanium has the formula(CH₃)₃CTi(N(CH₃)₂)₃. FIG. 2 depicts the structural formula oftertiary-butyltris-dimethylamido-titanium. It will be noted that onedimethylamido group of the tetrakis-dimethylamido-titanium molecule hasbeen replaced with a tertiary butyl group. The tertiary butyl group ismore easily removed from the molecule not only because it is larger thanthe dimethyl amido group, but because the carbon-titanium bond is weakerthan the nitrogen-titanium bonds. The resultant molecule is morereactive than tetrakis-dimethylamido-titanium and, in a chemical vapordeposition reaction, should produce films having a lower percentage ofcarbon impurities. The deposition temperature, which is dependent on thenitrogen source, is within a range of 350° C. to 700° C. The low end ofthe temperature range utilizes nitrogen-containing gases such asdiatomic nitrogen, ammonia, amides, amines and hydrazine which have beenconverted to a plasma. The higher end of the temperature range relies onthermal decomposition of the nitrogen source for the production ofreaction-sustaining radicals. In such a case, the use of diatomicnitrogen gas is precluded because of its high dissociation temperature.

Other materials may be incorporated in the titanium nitride films duringeither embodiment of the deposition process as heretofore described. Forexample, a titanium nitride film incorporating aluminum and having thegeneral formula TiAlN may be deposited by introducingaluminum-containing compounds such as aluminum chloride (AlCl₃)dimethylethylamidoalane (DMEAA) or dimethylaluminumhydride (DMAH) alongwith the TBTDMAT and nitrogen-containing compounds. Additionally, atitanium nitride film incorporating tungsten and having the generalformula TiNW may be deposited by introducing tungsten halide compoundssuch as WF₆ or WCl₆ or an organo-metallic compound such asbis(2,4-dimethylpentadienyl)tungsten along with the TBTDMAT andsilicon-containing compounds. The aluminum-containing compounds ortungsten-containing compounds may be introduced in a manner similar tothat of the other reactants using the temperature guidelines heretoforeprovided for each embodiment of the invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the drawings, which illustrate what is currently considered to be thebest mode for carrying out the invention:

FIG. 1 is a structural diagram of tetrakis-dialkylamido-titanium;

FIG. 2 is a structural diagram oftertiary-butyltris-dialkylamido-titanium; and

FIG. 3 is a block schematic diagram of a low-pressure chemical vapordeposition reactor system.

DETAILED DESCRIPTION OF THE INVENTION

A new low-pressure chemical vapor deposition process for depositinghighly conformal titanium nitride films having carbon impurities of lessthan 5% by weight and oxygen impurities of less than 10% by weight andhaving sheet resistance values within a range of about 1 to 10 ohms persquare will be described in reference to the low-pressure chemical vapordeposition reactor system depicted in FIG. 3.

A first embodiment of the invention which utilizes a cold-wall plasmaenhanced chemical vapor deposition (PECVD) process will be describedwith reference to FIG. 3. Although the following description of theprocess represents what the inventor believes is the preferredembodiment of the process, the process may be practiced in eithercold-wall or hot-wall plasma-enhanced chemical vapor depositionchambers, with or without premixing of the reactants. Furthermore,although the invention is directed to a technique for depositingconformal titanium nitride layers for use in the manufacture ofintegrated circuits, the process is also applicable to the deposition oftitanium nitride on substrates other than semiconductor wafers.

Referring now to FIG. 3, a tertiary-butyltris-dimethylamido-titaniummetal-organic source gas is produced by heating liquidtertiary-butyltris-dimethylamido-titanium (the metal-organic precursorcompound). The gas phase metal-organic compound transported by a carriergas is admitted into a pre-mixing chamber 3 through control valve 1 anda nitrogen-containing gas such as N₂, NH₃, a hydrazine, an amide or anamine (or some combination thereof) is admitted into the pre-mixingchamber 3 through control valve 2. Use of a carrier gas may also bedesired for the transport of certain amides or amines. The carrier gasesemployed may be H₂, N₂, He or Ar. In the case where N₂ is utilized as acarrier gas for the metal-organic compound, no other nitrogen-containinggas is required. Following the pre-mixing of the gas phase metal-organiccompound and the nitrogen-containing compound in pre-mixing chamber 3,the pre-mixed gases are admitted to the deposition chamber 4.Optionally, the gas-phase metal-organic compound may be mixed with aninert carrier gas by bubbling the carrier gas through the heatedmetal-organic compound. As a further option, the liquid metal-organiccompound may be converted to a fine spray or mist by a liquid injector(not shown). The mist is then passed through a vaporizer chamber (alsonot shown) en route to the deposition chamber. Within the depositionchamber 4, a semiconductor wafer 5 is heated to a temperature within arange of about 350° C. to 500° C. by convection from substrate holder 6(such as a graphite or alumina boat) that, in turn, is heated viahalogen lamps 7. The walls of the chamber are maintained at atemperature which is sufficiently high to prevent condensation ofTBTDMAT molecules thereon, yet not so high that decomposition of TBTDMATmolecules will occur. In a cold-wall reactor, the wafer is maintained ata temperature that is considerably higher than that of the chamberwalls, thereby minimizing deposition of titanium nitride on the chamberwalls. As a general rule, the chamber walls should be maintained withina range of about 50° C. to 400° C., and optimally within a range ofabout 100° C. to 200° C.

Still referring to FIG. 3, the pre-mixed combination of metal-organiccompound, one or more carrier gases and molecules of anitrogen-containing gas such as N₂, NH₃, hydrazine, amides and aminesenter deposition chamber 4 through shower head 15. A radio-frequency(RF) voltage, supplied by radio-frequency generator 8, is appliedbetween substrate holder 6 and deposition chamber wall 16, thus forminga plasma in which some of the metal-organic molecules andnitrogen-containing molecules are converted to radicals, ions, andmetastables. An RF power density of about 1 to 2 watts/cm² is applied tothe wafer in order to generate the plasma. Other remote plasmageneration systems, such as a microwave plasma generator, can also beused with comparable results. Metal-organic compound molecules areadsorbed on the surface of the wafer 5, and nitrogen-containing radicalsreact with the adsorbed metal-organic molecules to form a uniformlythick titanium nitride layer on the surface of the wafer.

As an alternative to the procedure employed above for the firstembodiment of the process, a remote source PECVD reactor may be employedwith similar results. In such a case, only the nitrogen-containing gasneed be passed through the plasma generator; the metal-organic compoundmay bypass the plasma generator en route to the deposition chamber 4.

Although the desired reaction may be effected at a pressure within arange of about 0.1 torr to 100 torr, a preferred range is deemed to beabout 0.2 torr to 10 torr. A constant deposition pressure within thatpreferred range is monitored and maintained by conventional pressurecontrol components consisting of pressure sensor 9, pressure switch 10,air operating vacuum valve 11 and pressure control valve 12. Thebyproducts of the reaction and the carrier gases (if carrier gases areused) pass through particulate filter 13 and escape through exhaust vent14 with the aid of a blower 17 to complete the process.

The deposited titanium nitride films can be annealed in anitrogen-containing ambiance at temperatures within a range of 400° C.to 700° C. Additionally, the deposited films can be annealed in a plasmaenvironment, which typically reduces carbon and oxygen impurities in thefilms, thereby decreasing resistivity of the films by as much as 50percent.

A second embodiment of the invention will also be described withreference to the diagrammatic representation of the chemical vapordeposition chamber of FIG. 3. However, for this embodiment, no RF poweris applied between the substrate holder 6 and the chamber wall 16.Instead, increased wafer temperature is relied on to effect a reactionbetween the tertiary-butyltris-dimethylamido-titanium and thenitrogen-containing gas. Diatomic nitrogen gas, because its dissociationtemperature is greater than temperatures compatible with semiconductorprocessing, is not used for the second embodiment of the process. Exceptfor the use of higher temperatures within a range of about 500° C. to700° C. and the lack of a plasma-generating RF power, other features ofthe process remain the same.

Other materials may be simultaneously incorporated in the titaniumnitride films during either embodiment of the deposition process asheretofore described. For example, a titanium nitride film incorporatingaluminum and having the general formula TiAlN may be deposited byintroducing aluminum-containing compounds such as aluminum chloride(AlCl₃) dimethylethylamidoalane (DMEAA) or dimethylaluminum-hydride(DMAH) along with the TBTDMAT and nitrogen-containing compounds. Thealuminum-containing compound may be introduced in a manner similar tothat of the other reactants using the temperature guidelines heretoforeprovided for each embodiment of the invention. Additionally, a titaniumnitride film incorporating tungsten and having the general formula TiWNmay be deposited by introducing organo-metallic compounds such asbis(2,4-dimethylpentadienyl)tungsten or tungsten halide compounds suchas WF₆ or WCl₆ along with the TBTDMAT and silicon-containing compounds.The aluminum-containing compounds or the tungsten-containing compoundsmay be introduced in a manner similar to that of the other reactantsusing the temperature guidelines heretofore provided for each embodimentof the invention.

While several embodiments of the process for depositing titanium nitrideusing tertiary-butyltris-dimethylamido-titanium as a precursor compoundhave been disclosed herein, it will be obvious to those having ordinaryskill in the art that modifications and changes may be made theretowithout affecting the scope and spirit of the invention as claimed.

What is claimed is:
 1. A chemical vapor deposition method comprising:placing a substrate in a chemical vapor deposition chamber to bemaintained at a subatmospheric pressure level; premixing atertiary-butyltris-dimethylamido-titanium compound and anitrogen-containing gas in a premixing chamber, said nitrogen-containinggas including other gases; admitting said premixedtertiary-butyltris-dimethylamido-titanium compound andnitrogen-containing gas into said chemical vapor deposition chamber;providing a plasma generation system for forming a plasma: forming aplasma in said chemical vapor deposition chamber when maintained at asubatmospheric pressure level, said plasma comprising saidtertiary-butyltris-dimethylamido-titanium compound and saidnitrogen-containing gas; heating said substrate to a temperature rangingfrom about 350° C. to about 700° C. for subjecting said substrate tosaid plasma; and depositing a predominantly titanium nitride film on aportion of said substrate, said predominantly titanium nitride filmhaving less than about 5% carbon impurities by weight and a sheetresistance of approximately 1 to 10 ohms per square.
 2. The method ofclaim 1, wherein said placing said substrate within said chemical vapordeposition chamber to be maintained at said subatmospheric pressurelevel comprises placing a semiconductor material selected from the groupconsisting of silicon, germanium, and gallium arsenide.
 3. The method ofclaim 1, wherein said admitting nitrogen-containing gas into saidchemical vapor deposition chamber comprises admitting anitrogen-containing gas selected from the group consisting of ammonia,amides, amines, and hydrazine into said chemical vapor depositionchamber.
 4. The method of claim 1, further comprising transporting saidtertiary-butyltris-dimethylamido-titanium compound to said chemicalvapor deposition chamber including a carrier gas, said carrier gasincluding gas selected from the group consisting of N₂, H₂, He and Ar.5. The method of claim 1, wherein said predominantly titanium nitridefilm having less than about 5% carbon impurities by weight and a sheetresistance of approximately 1 to 10 ohms per square further comprises apredominantly titanium nitride film comprising less than 10% oxygenimpurities by weight.
 6. The method of claim 1, wherein said placingsaid substrate in said chemical vapor deposition chamber to bemaintained at said subatmospheric pressure level comprises placing asemiconductor wafer within a chemical vapor deposition chambermaintained at a subatinospheric pressure.
 7. The method of claim 1,further comprising admitting an aluminum-containing compound into saidchemical vapor deposition chamber in combination with saidtertiary-butyltris-dimethylamido-titanium compound and saidnitrogen-containing gas to include aluminum into said predominantlytitanium nitride film having less than about 5% carbon impurities byweight.
 8. The method of claim 7, wherein said admitting analuminum-containing compound into said chemical vapor deposition chamberin combination with said tertiary-butyltris-dimethylamido-titanium andsaid nitrogen-containing gas comprises admitting AlCl₃ into saidchemical vapor deposition chamber.
 9. The method of claim 7, whereinsaid admitting an aluminum-containing compound into said chemical vapordeposition chamber in combination with saidtertiary-butyltris-dimethylamido-titanium compound and saidnitrogen-containing gas comprises admitting dimethylethylamidoalane intosaid chemical vapor deposition chamber.
 10. The method of claim 7,wherein said admitting an aluminum-containing compound into saidchemical vapor deposition chamber in combination with saidtertiaiy-butyltris-dimethylamido-titanium compound and saidnitrogen-containing gas comprises admitting dimethylaluminumhydride intosaid chemical vapor deposition chamber.
 11. The method of claim 1,further comprising admitting a tungsten-containing compound into saidchemical vapor deposition chamber in combination with saidtertiary-butyltris-dimethylamido-titanium compound and saidnitrogen-containing gas for including tungsten into said predominantlytitanium nitride film having less than about 5% carbon impurities byweight.
 12. The method of claim 11, wherein said admitting atungsten-containing compound into said chemical vapor deposition chamberin combination with said tertiary-butyltris-dimethylamido-titaniumcompound and said nitrogen-containing gas comprises admittingbis(2,4-dimethylpentadienyl)tungsten into said chemical vapor depositionchamber.
 13. The method of claim 11, wherein said admitting atungsten-containing compound into said chemical vapor deposition chamberin combination with said tertiary-butyltris-dimethylamido-titanium andsaid nitrogen-containing gas comprises admitting a tungsten halidecompound selected from the group consisting of WF₆ and WCl₆ into saidchemical vapor deposition chamber.
 14. The method of claim 1, furthercomprising annealing said predominantly titanium nitride film havingless than about 5% carbon impurities by weight and a sheet resistance ofapproximately 1 to 10 ohms per square in a nitrogen ambiance.
 15. Themethod of claim 1, wherein said plasma generation system comprises oneof a radio-frequency generator and a microwave plasma generator.
 16. Amethod for forming a predominantly titanium nitride film on a substratein an enhanced chemical deposition chamber maintained at asubatmospheric pressure comprising: providing said substrate at atemperature within a range of about 350° C. to 700° C.; flowinggas-phase tertiary-butyltris-dimethylamido-titanium into said enhancedchemical deposition chamber; flowing a nitrogen-containing gas into saidenhanced chemical deposition chamber; generating a plasma in saidenhanced chemical deposition chamber in a presence of said gas phasetertiaiy-butyltris-dimethylamido-titanium and said nitrogen-containinggas; and depositing a predominantly titanium nitride film on a portionof said substrate, said predominantly titanium nitride film having adeposited sheet resistance of approximately 1 to 10 ohms per square. 17.The method of claim 16, wherein said flowing a nitrogen-containing gasinto said enhanced chemical deposition chamber comprises flowing anitrogen-containing gas selected from a the group consisting of diatomicnitrogen, ammonia, amides and amines.
 18. The method of claim 16,wherein said depositing said predominantly titanium nitride film on saidsubstrate comprises depositing a titanium nitride film containing lessthan 5% carbon impurities by weight and less than 10% oxygen impuritiesby weight.
 19. The method of claim 16, further comprising admitting analuminum-containing compound into said enhanced chemical depositionchamber in combination with said gas-phasetertiary-butyltris-dimethylamido-titanium and said nitrogen-containinggas, said aluminum-containing compound comprising one of AlCl₃,dimethylethylamidealane and dimethylaluminumhydride.
 20. The method ofclaim 16, further comprising admitting a tungsten-containing compoundinto said enhanced chemical deposition chamber in combination with saidgas-phase tertiary-butyltris-dimethylamido-titanium and saidnitrogen-containing gas, thereby incorporating tungsten into saidpredominantly titanium nitride film, said tungsten-containing compoundincluding one of bis(2,4-dimethylpentadienyl) tungsten and a tungstenhalide compound selected from the group consisting of WF₆ and WCl₆, intosaid enhanced chemical deposition chamber.